Cell Physiology and Membrane Transport

A comprehensive set of vocabulary flashcards covering cell structure, organelles, membrane transport mechanisms, and signal transduction pathways described in the lecture notes.

Cell Physiology

The study of the cell as the functional unit of a living organism.

Cytoplasm

The region outside of the nucleus composed of a gel-like fluid called cytosol in which the cell organelles are suspended.

Plasma (Cell) Membrane

A selectively permeable physical barrier between the intracellular fluid (ICF) and extracellular fluid (ECF) that maintains homeostasis and ion composition.

Amphipathic molecule

A molecule containing both polar (hydrophilic) and nonpolar (hydrophobic) regions, such as phospholipids and cholesterol.

Phospholipid bilayer

A double layer of lipid molecules where polar heads face the aqueous environment and nonpolar fatty acid tails form a hydrophobic core.

Cholesterol

An amphipathic steroid lipid in the plasma membrane that maintains proper membrane fluidity and exists in a nearly $1:1$ ratio with phospholipids.

Glycocalyx

A layer of carbohydrates linked to lipids or proteins on the outer surface of the plasma membrane.

Integral (Intrinsic) proteins

Amphipathic membrane proteins that comprise $70\%$ of all proteins and are either partially or completely (transmembrane) inserted into the phospholipid bilayer.

Peripheral (Extrinsic) proteins

Proteins that are not amphipathic and are attached to the outer or inner surface of the membrane without penetrating the bilayer.

Desmosomes

Adhering junctions made of plaques, cadherins, and intermediate filaments that anchor cells together in tissues subject to mechanical stress.

Tight junctions

Impermeable junctions found in epithelial tissue made of occludins that limit the movement of molecules between cells.

Gap junctions

Communicating junctions made of proteins called connexons that electrically and metabolically couple adjacent cells by allowing ions and small molecules to move through them.

Chromatin

The combination of DNA and associated proteins found within the nucleus.

Nuclear Envelope

A double-layered porous membrane surrounding the nucleus composed of two phospholipid bilayers.

Nucleolus

The specific site within the nucleus where the synthesis of ribosomal RNA occurs.

Ribosomes

Non-membrane bound organelles composed of a small and large subunit that function in protein synthesis.

Rough Endoplasmic Reticulum (RER)

A system of flattened sacs with attached ribosomes that synthesizes proteins and performs post-translational modifications.

Smooth Endoplasmic Reticulum (SER)

A branched tubular structure that synthesizes lipids, stores calcium (as the sarcoplasmic reticulum in muscle), and performs drug detoxification in the liver.

Golgi apparatus

An organelle composed of flattened sacs called cisternae that modifies, sorts, and packages proteins received from the RER into vesicles.

Lysosomes

Organelles containing hydrolytic enzymes active at pH $5.0$ that degrade debris, bacteria, and viruses.

Peroxisomes

Organelles containing oxidative enzymes to break down fatty acids and alcohol, using catalase to neutralize the by-product hydrogen peroxide into water and oxygen.

Mitochondria

Organelles with a double phospholipid membrane and their own DNA that produce ATP through cellular respiration, featuring an inner membrane folded into cristae.

Cytoskeleton

A non-membrane bound organelle composed of protein filaments (microfilaments/actin, intermediate filaments, and microtubules/tubulin) that maintains cell shape and mediates motility.

Endocytosis

The uptake of material into the cell using vesicles that pinch off from the plasma membrane.

Phagocytosis

A type of endocytosis known as "cell eating" where pseudopodia surround large particles or bacteria to form a phagosome.

Pinocytosis

A nonspecific type of endocytosis known as "cell drinking" where the plasma membrane indents to ingest extracellular fluid and small dissolved molecules.

Receptor-mediated Endocytosis

A specific transport process involving receptors and the protein clathrin to concentrate and internalize specific ligands into the cell.

Exocytosis

The release of material from the cell using vesicles that fuse with the plasma membrane to secrete substances or add membrane components.

Chemical Driving Force

A force driven by a concentration gradient that moves molecules passively from high to low concentration.

Electrical Driving Force

A force due to the membrane potential and separation of charge that pushes or pulls charged substances across the membrane.

Equilibrium Potential

The condition where the chemical and electrical driving forces are equal and opposite, resulting in no net electrochemical driving force.

Simple Diffusion

The passive movement of small, nonpolar, or uncharged molecules through the lipid bilayer without the input of energy.

Osmosis

The net movement of water across a selectively permeable membrane from a region of low solute concentration to high solute concentration.

Facilitated Diffusion

Passive mediated transport that uses specific carrier proteins (like GLUT) or ion channels to move substances down their concentration gradient.

Primary Active Transport

A transport process that uses energy directly from ATP to move substances against their gradient, such as the $Na^+/K^+$ pump moving $3\,Na^+$ out and $2\,K^+$ in.

Secondary Active Transport

A transport process that uses the energy from an ion moving down its electrochemical gradient (like $Na^+$) to drive another substance (like glucose or $H^+$) against its gradient.

Saturable transport

A characteristic of mediated transport where the rate plateaus once all binding sites on transport proteins are occupied.

Transcription factor

A chemical messenger, such as a steroid hormone, that binds to intracellular receptors to alter the rate of mRNA transcription in the nucleus.

First messenger

An extracellular chemical messenger that binds to a specific membrane-bound receptor.

Second messenger

A substance (like cAMP or calcium) that is generated or enters the cytoplasm following the binding of a first messenger to a receptor.

Adenylyl cyclase

A membrane-bound enzyme that catalyzes the conversion of cytosolic ATP into the second messenger cyclic AMP (cAMP).

Protein Kinase A (PKA)

An enzyme activated by cAMP that phosphorylates cellular proteins by transferring a phosphate group from ATP.

Calmodulin

A cytosolic protein that is activated by binding to calcium and subsequently activates a calmodulin-dependent protein kinase to produce a cellular response.